05000456/FIN-2009005-06
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Finding | |
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| Description | The inspectors identified a URI during their review of post maintenance testing for RCS RTD replacement that occurred during the Unit 2 RFO in October 2009. From October 28 to October 31, 2009, following the Unit 2 refuelling outage, the licensee performed RCS RTD cross-calibration. The cross-calibration was credited as a post maintenance test for several RCS RTDs that were replaced during the refuelling outage. Cross-calibration is a method where, rather than performing a standard calibration on each RTD, each RTD in a system is compared against the RTD group average. Outliers from the average may be replaced or have their scaling equation adjusted. At Braidwood, the outlier criteria is 0.5oF for narrow range RTDs and 4.0oF for wide range RTDs. On February 21, 1995, the licensee submitted a license amendment request to the NRC regarding elimination of the RTD bypass manifold and installation of thermowell-mounted dual element fast response RTDs to replace the bypass manifold. The amendment request indicated that cross-calibration would be used to calibrate the RTDs and to verify per TS requirements that there has not been unacceptable drift. The NRC approved the amendment request in a Safety Evaluation dated September 5, 1995, and referenced NUREG/CR-5560 in the discussion of instrument uncertainty and drift. Cross-calibration of RTDs is discussed in Section 23 of NUREG/CR-5560. The method for cross-calibration introduces inherent uncertainties that must be accounted for. These uncertainties are accuracy of measurement equipment, stability of plant conditions, and uniformity of the system temperature. The value of these uncertainties is provided in NUREG/CR-5560 with the total uncertainty as high as 0.1oC to 0.32oC. The licensee performs RTD cross-calibration in accordance with Procedure 2BwISR 3.3.1.10-1, Unit 2 RCS RTD Cross Calibration. During the review of this procedure and the data generated during the cross-calibration conducted in October 2009, it was not immediately clear that the uncertainties were included in the cross-calibration results. At the conclusion of the inspection period, the inspectors continue to review cross-calibration data and intend to continue discussions of the issue with NRC Instrument & Controls personnel. This issue is also applicable to Unit 1. Pending additional information, this issue will remain open. (URI 05000456/2009005-06; 0500457/2009005-06 |
| Site: | Braidwood  |
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| Report | IR 05000456/2009005 Section 1R19 |
| Date counted | Dec 31, 2009 (2009Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.19 |
| Inspectors (proximate) | A Garmoe B Dickson B Metrow B Palagi J Gall M Holmberg M Mitchell M Perry R Jickling R Ng R Skokowskin Shahr Langstaff J Robbins B Dickson M Perry A Garmoe R Skokowski C Scott |
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Finding - Braidwood - IR 05000456/2009005 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Braidwood) @ 2009Q4
Self-Identified List (Braidwood)
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